The present invention pertains to methods and systems for evaluating the structural integrity of electrically conductive structures and, more particularly, to such methods and systems wherein the electrical impulse response of the structure is measured after a test input signal is applied in order to assess the integrity of the structure and the presence, severity and location of any defects.
The prior art, as exemplified by U.S. Pat. No. 3,988,667 to Roth et al, No. 4,067,060 to Poussart et al, No. 4,275,446 to Blaess, No. 4,935,699 to Boenning, No. 4,988,949 to Boenning et al, No. 5,025,221 to Blaess, No. 6,064,212 to Ariweilar et al and No. 6,265,880 to Bornet et al and British Patent No. 1,160,271 to Booth et al, discloses the use of periodic-random, noise and pseudo-random binary sequence test input signals for measuring transfer functions of systems under test, and/or measuring transmission characteristics by Fourier analysis, and/or systems for detecting chafing of cables and/or conduits; however, the prior art does not permit implementation of high frequency evaluation for detecting subtle changes of electrical characteristics of structures to be tested or evaluated. In prior art methods for testing of servo systems, the impulse response function is compared with a set of known correct functions and any discrepancy is noted.
It is known that the cross correlation of a random noise input and the resulting output of a system is identical to the impulse response of the system. To be perfect, the random noise input would need to be infinitely long and perfectly random. In practice, a specific length, pseudo-random binary signal has been disclosed, as for example in the Booth et al British Patent No. 1,160,271, where the cross correlation function of the input with the output is generated by computing the average of the cross correlation of the output with a copy of the input delayed to generate one point on the impulse response function. An integrator is used to measure the average value of the impulse response; and, accordingly, the Booth et al system has the disadvantage of not being feasibly implemented for high frequency test signals.